1. Field of the Invention
The present invention relates to switch stands for railroad switches, and in particular to switch stands which permit trailing operation of railroad switches.
2. Description of the Related Art
On railroad tracks, railroad switches have been provided to permit trains to transfer from a track or set of rails to another based on the position of a pair of linked tapering rails or points. Railroad switches have also been referred to as turnouts. The switching capability has often been provided through an electric motor driven switch which included a motor-driven throw bar or the like to throw switch points to control the switching of rolling stock. Motor-driven switching worked well for main line and transit operations. However, in rail yard applications additional switching features were needed. It has been common for yard switch operations to include manual operation of the switches by yard personnel.
For accident prevention and safety purposes, it has been common practice to provide switch stands with a mechanism to lock the switch in a desired setting and to indicate that position. However, it has also been desirable that the switches also permit what is known as trailing, where rolling stock such as a car or engine could go through the switch from either of two merging sets of rails onto a single set of rails without having to change the set position of the switch.
In trailing operations, the force of the wheels changed the position of the points to the proper position for the switch point change to occur. If the switch stand was locked, an attempt at trailing would cause damage the switch and stand, and possibly even worse. For this reason, some forms of switch stands were provided with what was known as a semi-automatic capability. The stand was motor-driven and kept in a normal position, but was provided with a separate unit that permitted trailing.
For a switch machine with trailing capability, passage of rolling stock through the switch in the reverse or trailing direction caused the switch to be thrown automatically, that is, without the time delay of a manual switch operation.
So far as is known, two other types of switch stands have been commonly used for railroad switches. One type of switch was manually operable or changeable. Manual switch stands were provided with locks for safety purposes to set and retain the switch in its desired position or setting. However, if trailing operations were attempted through a locked switch, damage resulted as has been mentioned. It was also expensive and time consuming to unlock and then manually change the position of a manual switch temporarily for trailing to occur. However, safety considerations required that the switch be kept locked at all other times at its desired or normal setting.
The other type of switch stand has been the remote controlled or automatic switch stand which allowed the switch stand to be locked from a remote control site. These switch stands were even more costly than semi-automatic stands. Estimated costs of a single remote control switch stand have been about fifteen thousand dollars each. With the number of switch stands present in a railroad system, the capital investment costs can be seen to be considerable.